Labyrinth seals are widely used to surround rotatable shafts, and prevent leakage of oil from bearing housings. Generally, either parallel or thread-like teeth patterns are formed on the interior surfaces of these labyrinth seals. The tips of each tooth of the parallel and thread-like teeth patterns provide a radial clearance with respect to the rotatable shaft, and the channels formed between the teeth of these teeth patterns are used to capture the oil. However, even when using a thread-like teeth pattern, axial drain holes have universally been used to return the oil to the bearing housings. These axial drain holes are parallel to the axis of the rotatable shaft, and are drilled through each tooth of the teeth pattern except for tooth farthest removed from the bearing housing, the so-called terminal tooth. As such, the axial drain holes join the channels between the teeth.
The axial drain holes are intended to function to drain the oil that has migrated through the radial clearance between the rotatable shaft and the tips of the individual teeth back into the bearing housings. However, the use of axial drain holes has two limitations. First, when using axial drain holes, the pressures in the channels are equalized, and any pressure drop taken across the labyrinth seals is effectively taken entirely across the terminal tooth. Because the terminal tooth cannot withstand a significant pressure drop, these labyrinth seals cannot maintain a significant pressure drop between the interior and exterior of the bearing housing. Second, the axial drain holes actually siphon oil from the bearing housing into the channels formed between the individual teeth. Consequently, the axial drain holes actually interfere with the efficient return of the oil to the bearing housings, and contravene their very purpose.
Therefore, there is a need for additional improvements to labyrinth seals to reduce the amount of oil leakage from the bearing housings. Such improvements would eliminate the need for axial drain holes, and accommodate a significant pressure drop without adversely effecting the performance of the labyrinth seal.